<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="../vue.js"></script>
</head>

<body>
  <div id="app">
    <button @click = "isHot = !isHot">切换天气</button>
    <p>今天天气真{{isHot? "冷" : "热"}}</p>
    <img :src="src" >
  </div>
  <script>
    Vue.config.productionTip = false;
    
    const vm = new Vue({
      el: "#app",
      data() {
        return {
          isHot: true,
          src: './leng.gif'
        }
      },
      //watch配置项
      watch:{
        //监听isHot属性的变化
        isHot:{
          //当被监听的isHot发生改变的时候,handler函数就会执行
          handler(news){
            //isHot变化改变src
            this.src = news? "./leng.gif" : "./re.webp"
          }
        },
      }
    })
  </script>
</body>

</html>